This invention relates to an image forming method, and more particularly, to a method for forming an image by forming or releasing a diffusible dye in an alkaline atmosphere.
A variety of proposals have been made in the art for producing dye images through heat development. Among them, the most interested method capable of separating dye images from silver images in a simple, but complete manner is by using a dye-providing substance which forms or releases a diffusible dye through heat development and diffusing the diffusible dye into a dye-fixing or image-receiving element under the influence of heat and/or solvent to produce a dye image. Reference is made to U.S. Pat. Nos.
______________________________________ 4,463,079 4,474,867 4,478,927 4,483,914 4,507,380 4,500,626 ______________________________________
Japanese patent application Kokai Nos.
______________________________________ 58-149046 58-149047 59-152440 59-154445 59-165054 59-180548 59-168439 59-174832 59-174833 59-174834 59-174835 61-238056 and EP 210660A. ______________________________________
These prior art well-known methods for forming dye images through heat development, however, suffer from poor image discrimination in that a dye image available is rather stained and has a relatively low density.
One system uses a dye-providing substance in combination with a reducing agent. The reaction between the reducing agent or an oxidized form thereof and the dyereducing providing substance is utilized to form an imagewise distribution of a diffusible dye. In this case, an image is often obtained at a lower density than expected probably because a latent image is injured during heat development. In another system, a reducing agent is oxidized imagewise, and a dye-providing substance is reacted with that portion of the reducing agent which is left in a reverse-imagewise pattern to produce a positive imagewise distribution of a diffusible dye. Under high-temperature conditions during heat development, however, there is no substantial difference in reaction rate between the reaction of the silver halide or organic silver salt with the reducing agent and the reaction of the dye-providing substance with the reducing agent. Then, the reducing agent can react with the dye-providing substance to produce a diffusible dye even in an area where the silver halide is developed.